Proof of Interstitial Cobalt Defects in Silicon Float Zone Crystals Doped during Crystal Growth

Abstract

In Si crystals, which were doped with cobalt during floating- zone growth, mainly substitutional Co defects with a concentration of about 7 x 1012 cm-3 can be detected by deep- level transient spectroscopy. But a second fundamental defect with a lower concentration around 7 x 1011 cm-3 shows features, which are typical for an interstitial defect with a remarkable mobility even at room temperature. It has a donor level at EV + 0.31 eV as well as an acceptor level at EC - 0.4 eV and is attributed to interstitial Co. In p-type samples pairing of interstitial Co with boron acceptors is observed. The capture coefficient of this pairing reaction is thermally activated with a characteristic energy of 0.9 eV. A binding energy of the Co-B pairs of about 0.6 eV is obtained. In the upper half of the gap an acceptor level was observed at EC - 0.08 eV.